Chain tensioning device



April 12, 1966 H. WARD CHAIN TENsIoNme DEVICE Filed March 30, 1964 lnvenlor Ha %A\/ W100 WW Attorney 20a 8a /2a United. States Patent 3,245,277 CHAIN TENSIONING DEVICE Harry Ward, Hurstbourne Tarrant, near Andover Hampshire, England, assignor, by mesne assignments, to AME International Limited, London, England Filed Mar. 30, 1964, Ser. No. 355,869 Claims priority, application Great Britain, Apr. 5, 1963, 13,705/ 63 4 Claims. (Cl. 74-242.11)

According to this invention, a device for adjusting the tension in a chain running between two rotary members such as sprockets or rollers comprises an arm which in use is fixed in relation to the axes of the rotary members and lies substantially parallel to the line joining the axes of the rotary members, an arm lying in the same plane as the fixed arm and pivoted about an axis transverse to the fixed arm so that one end may swing either towards or away from the fixed arm but in use is constrained by a run of the chain in one direction of swing, and a slider bar extending between the fixed arm and the swinging arm and being biased away from the pivotal axis of the swinging arm in a direction generally parallel to the fixed arm, this slider bar including an end portion co-operating with the fixed arm so that it may slide along it, and an opposite end portion co-operating with the pivoted arm so that it may slide along it, whereby the biasing force acting on the slider bar is transmitted to the swinging arm so that the swinging arm is constrained to bear against the run of chain.

It the chain runs between two sprockets for example, one of which is at a higher level than the other, the fixed arm is also arranged with one end correspondingly higher than the other; the slider bar then runs up and down the fixed arm. Depending upon the inclination of the fixed arm to the vertical, the biasing force acting on the slider bar may be due entirely to the weight of the slider bar or may be assisted by a spring or other means. In the preferred arrangement, the two chain sprockets are one above the other, and the fixed arm is also vertical, so that one end of the slider bar runs up and down the fixed arm, and the slider bar is urged downwards by its own weight.

If the two sprockets are in the same horizontal plane, so that the runs of the chain are also horizontal, the slider bar may be biased in one direction by means of a spring.

Devices constructed according to the invention will now be described by way of example with reference to the accompanying drawings, of which:

FIGURE 1 shows a device in use for tensioning a chain running between two sprockets whose axes lie one above the other;

FIGURE 2 shows a diiferent device in use for tensioning a chain running between two sprockets whose axes lie in the same horizontal plane.

With reference to FIGURE 1, a chain has two runs between two sprockets, one of which is shown at 4, this sprocket 4 being pivoted about an axis 6. The tensioning device comprises a fixed arm 8 mounted upon a pin 10 and a bracket indicated generally at 12, a swinging arm 14 pivoted about a pin 16 mounted upon a main bracket 18 which also mounts the pin 10 and the bracket 12, and a slider bar 20 which extends between the fixed arm 8 and the swinging arm 14.

The slider bar 20 comprises two bars one of which is shown at 22, these bars being spaced apart by spacer bolts 24 and 26 at each end. The two bars of the slider bar pass outside both the fixed arm 8 and the swinging arm 14, so that the slider bar embraces both arms.

A block 32 mounted on the spacer bolt 26 and lying between the two bars of the slider bar 20 bears upon the outside edge 34 of the swinging arm 14, which outside edge 34 is suitably roughened. A similar block bears on a roughened edge 35 of the fixed arm 8. The weight of the slider bar 20 is transmitted to the swinging arm 14 so that a roller 36 at the lower end of the swinging arm 14 is biased inwards against the chain 2. The existing tension in the chain acts in the direction of the arrow 38, and the weight of the slider bar 20 acting upon the swinging arm 14 causes the roller 36 to bear upon the chain 2 with a force in the direction of the arrow 40; an equilibrium position of the chain 2 is quickly attained.

The bracket 12.comprises a threaded rod 42 which passes through a bore in the main frame 18 and is locked in position by means of lock nuts 46 and 48. The threaded rod 42 also passes through a bore 50 in the fixed arm 8, and a spring 52 acts between a side of the fixed arm 8 and a collar 54 which is mounted on the threaded rod 42 and locked in position by means of a nut 56. Further lock nuts 58 and 60 determine the position along the threaded rod 42 at which the fixed arm 8 is mounted, and consequently the degree of compression. of the spring 52.

Commercially produced driving chains frequently have errors of pitch; these errors are normally offset by selection of the links to compensate for them. The errors are thus balanced out over a series of links, so that a given chain will have phases of slackness and tightness as it runs past a particular point. Since the action of the slider bar on the swinging arm 14 is irreversible, if the position of the fixed arm 8 is fixed rigidly excessive tension occurs in a chain at regions where it is very tight. The arrangement of the brackets 12 described above allows the fixed arm to breath slightly in response to the phases of slackness and tightness in any given chain, and so avoids the setting up of excessive tension in the chain. The life of any given chain is thereby considerably increased.

During servicing of the chain drive, the tension may be released by lifting the slider bar and supporting it temporarily on a pin 28 which may be put in any one of a number of holes 30 spaced out along the length of the fixed arm 8.

FIGURE 2 shows a device similar to that shown in FIGURE 1, except that it is used for adjusting the ten sion in a chain running between two sprockets and 72 with axes lying in the same horizontal plane. Similar parts of the device are identified by the same numerals as used in FIGURE 1, but with the addition of a sufiix a.

The fixed arm 8a is mounted horizontally as shown. A mounting bracket 74 extends from the main bracket 18a, and a spring 76 extends from the end of the bracket 74 to the centre of the slider bar 20a. This spring 76 acts to bias the slider bar away from the pivotal axis 16a of the swinging arm 14a, and acts analogously to the gravitational force acting on the slider bar 20 in the arrangemnt shown in FIGURE 1.

In an alternative arrangement, the lower end of the swinging arm 14 is arranged to engage against the inside of a run of the chain, in order to urge that run of the chain outwards. Such an arrangement is particularly desirable if the chain sprockets are spaced apart by a distance which is large compared with their diameters, as there is then no possibility of the runs of the chain touching if the chain becomes very slack.

In a further alternative arrangement, the spacer bolt 26 runs within a slot cut along the length of the swinging arm 14, and bears against a side of this slot in order to bias the swinging arm in the required direction.

In use, a chain will become progressively more slack, as its over-all length increases. When a device according to the invention is used for adjusting the tension, the slider bar 20 will slide down the swinging arm 14 as the 3 length of the chain increases, and the roller 36 will be moved so as to move the chain in order to take up any extra slackness in it.

I claim:

1. A device for adjusting the tension in a chain running between two rotary members comprising an arm fixed in relation to the axes of the rotary members and lying substantially parallel to the line joining the axes of the rotary members, a swinging arm lying in the same plane as the fixed arm and pivotal about an axis transverse to the fixed arm so that one end may swing either towards or away from the fixed arm and constrained by a run of the chain in one direction of swing, and a slider bar extending between the fixed arm and the swinging arm and being biased away from the pivotal axis of the swinging arm in a direction generally parallel to the fixed arm, said slider bar including an end portion cooperating with the fixed arm so that it may slide along it, and an opposite end portion co-operating with the swinging arm so that it may slide along it, whereby the biasing force acting on the slider bar is transmitted to the swinging arm so that the swinging arm is constrained to bear against the run of the chain.

2. A device according to claim 1 in which the fixed arm has one end higher than the other, and the slider bar is biased away from the pivotal axis of the swinging arm by its own weight.

3. A device according to claim 2, in which the fixed arm is vertical.

4. A device according to claim 1 in which the slider bar is biased in one direction by means of a spring.

References Cited by the Examiner UNITED STATES PATENTS 1,379,055 5/1921 Smith 74-24211 X 2,066,721 1/1937 Eaton 74242.l1 X 2,110,439 3/1938 Gordon 74242.ll 2,663,195 12/1953 Horan 74242.ll

DON A. WAITE, Primary Examiner. 

1. A DEVICE FOR ADJUSTING THE TENSION IN A CHAIN RUNNING BETWEEN TWO ROTARY MEMBERS COMPRISING AN ARM FIXED IN RELATION TO THE AXES OF THE ROTARY MEMBERS AND LYING SUBSTANTIALLY PARALLEL TO THE LINE JOINING THE AXES OF THE ROTARY MEMBERS, A SWINGING ARM LYING THE SAME PLANE AS THE FIXED ARM AND PIVOTAL ABOUT AN AXIS TRANSVERSE TO THE FIXED ARM SO THAT ONE END MAY SWING EITHER TOWARDS OR AWAY FROM THE FIXED ARM AND CONSTRAINED BY A RUN OF THE CHAIN IN ONE DIRECTION OF SWING, AND A SLIDER BAR EXTENDING BETWEEN THE FIXED ARM AND THE SWINGING ARM AND BEING BIASED AWAY FROM THE PIVOTAL AXIS OF THE SWINGING ARM IN A DIRECTION GENERALLY PARALLEL TO THE FIXED ARM, SAID SLIDER BAR INCLUDING AN END PORTION COOPERATING WITH THE FIXED ARM SO THAT IT MAY SLIDE ALONG IT, AND AN OPPOSITE END PORTION CO-OPERATING WITH THE SWINGING ARM SO THAT IT MAY SLIDE ALONG IT, WHEREBY THE BIASING FORCE ACTING ON THE SLIDER BAR IS TRANSMITTED TO THE SWINGING ARM SO THAT THE SWINGING ARM IS CONSTRAINED TO BEAR AGAINST THE RUN OF THE CHAIN. 